Towards ground truthing exploration in the central Arctic Ocean: a Cenozoic compaction history from the Lomonosov Ridge

Abstract

The Integrated Ocean Drilling Program's Expedition 302, the Arctic Coring Expedition (ACEX), recovered the first Cenozoic sedimentary sequence from the central Arctic Ocean. ACEX provided ground truth for basin scale geophysical interpretations and for guiding future exploration targets in this largely unexplored ocean basin. Here, we present results from a series of consolidation tests used to characterize sediment compressibility and permeability and integrate these with high‐resolution measurements of bulk density, porosity and shear strength to investigate the stress history and the nature of prominent lithostratigraphic and seismostratigraphic boundaries in the ACEX record. Despite moderate sedimentation rates (10–30 m Myr−1) and high permeability values (10−15–10−18 m2), consolidation and shear strength measurements both suggest an overall state of underconsolidation or overpressure. One‐dimensional compaction modelling shows that to maintain such excess pore pressures, an in situ fluid source is required that exceeds the rate of fluid expulsion generated by mechanical compaction alone. Geochemical and sedimentological evidence is presented that identifies the Opal A–C/T transformation of biosiliceous rich sediments as a potential additional in situ fluid source. However, the combined rate of chemical and mechanical compaction remain too low to fully account for the observed pore pressure gradients, implying an additional diagenetic fluid source from within or below the recovered Cenozoic sediments from ACEX. Recognition of the Opal A–C/T reaction front in the ACEX record has broad reaching regional implications on slope stability and subsurface pressure evolution, and provides an important consideration for interpreting and correlating the spatially limited seismic data from the Arctic Ocean.

Depositional Evolution of the Western Amundsen Basin, Arctic Ocean: Paleoceanographic and Tectonic Implications

“…O'Regan et al () suggested that the ridge remained at or near sea level during the duration of the time gap. Based on an analysis of the consolidation, strength, and permeability of the sediments recovered, O'Regan et al () suggest that the hiatus arose from a period of prolonged low to nondeposition. The cause of nondeposition and/or erosion has been attributed to tectonic uplift, either as a result of mantle phase changes (Minakov & Podladchikov, ) or as a result of the Eurekan orogeny, which reached its peak during the Eocene (Døssing et al, ).…”

Deep water methane hydrates in the Arctic Ocean: Reassessing the significance of a shallow BSR on the Lomonosov Ridge

“…There are three primary petrophysical properties that are required to calculate heat flow from a BSR; the compressional wave velocity, bulk density and thermal conductivity. In this model we use published compaction trends from sediments at ACEX [ O'Regan et al , 2010] to develop a porosity‐depth function, and use this to calculate the integrated density and thermal conductivity of the overlying sediment column. Each of the steps and assumptions in constructing the model are outlined below.…”

“…Concordant with this observation is a more gradual change in the modeled compressional wave velocities, which led to the suggestion that this segment of the Lomonosov Ridge was at initially deeper water depths during rifting from Barents‐Kara shelf [ Jokat , 2005]. Within seismic Unit I there is no indication of either an unconformity or a large‐scale shift from biosiliceous to glaciomarine sediments in the interpreted Cenozoic cover, and it remains possible that the current boundary between the two primary seismic units is younger, and is related to either the end of basin‐wide biosiliceous and organic rich sedimentation in the middle Miocene or alternatively represents the ongoing conversion of Opal A to C/T [ O'Regan et al , 2010]. However, irrespective of the age of this boundary, the BSR identified on these lines occurs at a relatively constant depth of ∼200 ms, and falls near the top of the Cenozoic sequence within Miocene or younger sediments (Figure 2).…”

Hemipelagic deposits on the Mendeleev and northwestern Alpha submarine Ridges in the Arctic Ocean: acoustic stratigraphy, depositional environment and an inter-ridge correlation calibrated by the ACEX results

“…However, the latter correlation is of questionable value as the late Paleocene-early Eocene depositional environment on the shallow Lomonosov Ridge most likely differed from the older and deeper Mendeleev and Alpha Ridges. Also the thermal and subsidence history of Lomonosov Ridge are different from Mendeleev and Alpha Ridges and leave open any associations of the lower reflection bands on Mendeleev and Alpha Ridges with Opal A to Opal CT transition as suggested for Unit 2/3 transition in the ACEX core from Lomonosov Ridge (O'Reagan et al 2009). The age of the oldest sediments above acoustic basement on the Mendeleev and northwestern Alpha Ridges is estimated to be *70-75 Ma from the thickness (*0.20-0.25 s) below the top of MRB2 and ARB3 (Fig.…”

“…These upper layers isolate the warmer, more saline waters of Atlantic origin below and inhibit melting of the sea ice cover. The oceanic circulation in the present Arctic Ocean is characterized by low kinetic energy and weak cyclonic boundary currents (Rudels et al 1994;Jones 2001;Woodgate et al 2007). The boundary current flow (Fig.…”